Capillary Electrophoresis for the Forensic Analysis of Ball-point Inks Extracted from Paper

Joanna Mania, Joanna Bis, Paweł Kościelniak

Abstract

One of the important tasks of a questioned document examiner is the discrimination, comparison and identification of inks. For these aims the analysis of dyes used as colouring material in inks can be applied. Up to now mainly two techniques: thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC) were used in this area.

Capillary electrophoresis (CE) is a relatively new analytical technique characterized by a high-resolution separation power. This technique has been already applied to the analysis of various dyes, including dyes used as ink components.

In 2000 and 2001 the method for analysis of various kind of inks extracted from paper were developed and optimized in the Laboratory for Forensic Chemistry at Jagiellonian University. The analyses were performed in fused silica capillaries (50mm I.D., 85 cm/52 cm total/effective length) using PrinCE 550 CE System. The separation solution was composed of 30% (volume) of acetonitrile and contained 42 mM of SDS, 10.5 mM of 3-AP, 5.25 mM of HCl, 0.35 mM of Brij-35 per 1 L.

The aim of presented studies was to improve analytical conditions for the separation and identification of blue ink dyes. Several blue dyes and blue ball-point pen inks of different origin extracted from paper were analyzed. The separations were reproducible and led to base line resolution for almost all components. Received electropherograms shows distinctive differences between inks of different manufactures.